1. Field of the Invention
This invention pertains generally to multilayer polymer films and methods for producing the same.
2. Description of the Prior Art
Various polymer films are utilized as packaging materials to provide a sealed package for food and other products. Such films may be transparent to allow inspection by the consumer of the product through the film, but to nonetheless seal out air and seal in moisture and juices. Polymer films such as sarans and polyethylene, and various modifications thereof, have proven useful in food packaging.
Often, the various desirable characteristics that a packaging film must provide are not attainable in a film composed of a single polymer material. For example, relatively high tensile strengths and moisture and oxygen impermeability is desired in films which are utilized to package meat products. Various nylon resins may be utilized to form such high tensile strength oxygen impermeable films since nylon yields one of the strongest of the commonly utilized films. However, nylon is not easily heat sealed to itself with conventional sealing equipment, and must be adhered to itself with adhesives or at relatively high temperatures that may affect the food material that is being packaged. To provide the desirable strength properties of nylon in combination with the relatively low temperature heat sealing properties of other polymers, attempts have been made to combine nylon layers with layers of easily heat sealed polymers such as ionomers (metal salt neutralized copolymers of ethylene and acrylic acid or methacrylic acid, available from DuPont under the name Surlyn). It has been found that nylon is a difficult material with which to form strong multilayer films, and generally poor adhesion between the nylon layer and the other polymer layers results. Moreover, the other polymers utilized, such as ionomer, are often subject to degradation of the adhesive bond between the nylon and the polymer in the presence of high moisture and elevated temperatures. Such materials thus may be subject to delamination when used for the packaging of moist materials such as fresh meats.